Safety control for fuel burners



July 27, 1948v c. K. s'rRoBEl. 2,445,341

SAFETY CONTROL FOR FUELBURNERS Filed Aug. 16, 1943 Swej; '12 Handy@ Charla/li Swbel.

H] ATTORN EY Patented VJuly 27, 1948 SAFETY CONTROL FOR FUEL BURNEBS Charles K. Strobel, Pittsburgh, Pa., assignor to Bobertlhaw-Fulton Controls Company, a corporation of Delaware ApplicationAugust 16, 1943, Serial No. 498,749

12 Claims. (Cl. 158-1171) This invention relates to safety control apparatus for fuel burners and, more particularly, to electrically operated controls therefor.

In copending application Serial No. 463,492, filed October 27, 1942, there is disclosed safety control apparatus of the kind described having burner ignition means which becomes deenergized during normal running of the burner and which becomes reenergized after the safety control has operated. In the system of the prior application the reenergizing of the igniter is delayed for a sufficient period of time to permit unburned fuel remaining from the previous operation to escape. However, as soon as conditions permit, an identical series of operations occurs before the running condition of the burner is attained regardless of the period of time between the recycling operations. l

The system operating as described may be adjusted to perform satisfactorily over a primary voltage range of 105 to 125 volts and speedy response to control conditions be obtained. Necessarily, a high degree of sensitivity to fluctuations in current values is required in the circuit to obtain the desired operating times and such arrangement introduces objectionable vibration into certain operating parts. The noise so created may be particularly pronounced during the starting and stopping periods of the safety apparatus, although under normal running conditions extremely quiet operation is obtained.

In this invention various modications have been made to the original system With one object of shortening the over-all recycling time.

Another object ofthe invention is to eliminate objectionable noise in operation of the safety system.

Another object of the invention is to reduce the time for starting the burner in operation to a minimum.

A further object of the invention is to preserve the required purge period while achieving the foregoing objects.

Other advantages and objects will become apparent from the following description t'aken in connection with the accompanying drawing which is a schematic view of a safety control apparatus for a gaseous fuel burner embodying this invention.

Referring more in detail to the drawing, a gaseous fuel burner Il is supplied with fuel from a main fuel pipe I2. The fuel supply is controlled by a main valve I4 which, in this instance, is adapted for manual operation but which may be arranged for thermostatic operation if desired.

Preferably, a main switch for the electric circuit to be described is included in the main valve I4 and is arranged to establishthe circuit whenever the valve is open. Interposed in the fuel supply pipe I2 between the main valve I4 and the bur'ner I0 is an electromagnetic gas valve I8 of any suitable type which may be arranged, as in this instance, to be opened by energization of the electromagnet and closed by gravity upon deenergization thereof. i

A pilot burner I3 is supplied with fuel from a conduit 20 connected to the main valve I4 to receive fuel from the pipe I2 when the main valve is open. The pilot burner is adapted to be ignited by an electric igniting means 22, such as an igmtion coil and, in turn, will ignite the fuel issuing from the main burner III when in operation. Electrical energy for the operation of the electromagnetic valve I6 and the igniting means 22 is supplied through line wires 24-26 connected to the primary of a transformer 28.

Operation of the electromagnetic valve I6 and ignition means 22 is controlled by switching means in the form of a control relay 30. This relay includes a magnetizable core 32 having the usual coil 34 associated therewith and is shown as adapted to attract a pair of armature members 36 and 38 when suitably energized. The armatures 36 and 38 may be mounted for movement toward and away from the core 32 and are adapted to return to a normal positioning by gravity, springs or other means (not shown). In this normal position of the armature 36, that is, when the operating means is deenergized, engagement is made by a contact 40 thereon with a fixed contact 42. In addition to the contact 40, the armature 36 carries on the opposite side thereof a contact 48 which is adapted to engage with a xed contact 52 when the armature 36 moves from normal to attracted position. It will be apparent that upon such movement the contacts 40 and 42 `are then disengaged. In similar manner armature 38 carries contact 50 which is adapted for engagement with xed contact 54. 7

A heat responsive or flame sensitive element 56 is positioned to be exposed to the flame of the pilot burner I8 for causing operation of the relay 30 to move the armatures thereof from one position to the other. The flame sensitive element 56 may take the form of ya coil of wire of material having normally a relatively low resistance and a. positive temperature coeiilcient of resistance. Such devices commonly termed ballast resistors are thermally responsive to the passage of current therethrough but, in this embodiment, the element B, hereinafter termed the ballast resistor, is primarily responsive to the heat of the pilot burner flame. Accordingly, it wil] be understood that it is the variation in resistance in response to the pilot burner name which renders the ballast resistor 58 useful in this invention.

As indicated in the drawing. the main burner l0, pilot burner I8, ignition means 22 and ballast resistor 356 are adapted to be mounted in the chamber 58 of an oven or like device. In such arrangements in case of flame failure unburned fuel may be present in the vicinity of the main burner I 0 following closure of the electromagnetic valve I6 and such fuel should be permitted to ilow away before the ignition means is energized to ignite the pilot burner. To this end, a purge penod is provided in the sequence of operation o1 the control by a thermally operated switch @d which maintains the ignition means 22 inoperative for a predetermined period following closure of the electromagnetic valve it. The switch tu comprises a bimetal element 52 carrying a contact 64 which is adapted to move therewith and engage a ilxed contact 66 when the bimetal element 62 is unheated, these contacts becoming disengaged whenever the bimetal is sufficiently heated.

Adjustment-of the igniter current value in the system may be' obtained by the provision of an adjusting resistor lll, which is preferably of fixed impedance value. A pilot signal lamp l2 may be included to aiord visual indication of normal running operation of the system. A cut-out 'ii is incorporated to protect against the continued escape of unburned fuel which might loev caused by simultaneous failure of the ignition means 22 and the relay 30. A large steady electrical current through the ballast resistor 56 which, in such event, would remain unheated by a ame will cause the cut-out to operate, although a large inrush current will not cause such operation. Hence, the cut-out 'it is preferably of the thermal type provided with time-lag operation having predetermined time current characteristics and usually containing a heater element in addition to and aiecting a fusible member which opens the circuit upon an over-current.

In order that the system may be operated in the event of failure of the ignition means 21?, a switch i6 for manual operation is provided together with a. iixed resistor l@ equivalent in im pedance value to the ignition means As will be apparent hereinafter, these elements may be utilized in place of an inoperative ignition means 22 and permit the pilot burner it to be ignited by a match to place the system in normal operating condition without the recycling feature.

. rihis invention is particularly concerned with the length of time that it takes the apparatus to recycle and the equally important feature of noise reduction. A simple means of shortening the operating time and reducing ,noise in operation comprises introducing a resistor il@ of iixed value across the relay coil 3&3 to vary the sensitivity thereof at appropriate times. It will be apparent that this resistor dll could be permanently connected across the relay coil 3d but, in this embodiment, it is operable by a bimetal switch d2 comprising a -bimetal element tl carrying a contact t@ which is adapted to move therewith and engage a fixed contact iid when the bimetal element Sii is suicently heated. It will be apparent that the contacts G-d become disengaged whenever the bimetal element d is unheated.

The apparatus is shown in the normal running position of the main burner I0 in which the electromagnetic valve I6 is energized and the ignition means 22 deenergized that is, with the main burner l0 operating and the pilot burner I8 producing a ilame. At the start of operation to obtain this running position the circuit elements are cold and the control relay occupies the normal position shown, exceptthat the contacts B6' and 64 of the purge bimetal switch 80 are closed. The contacts 86 and 88 of the shunting bimetal switch 82 are open as'shown. Opening of the main valve I4 permits fuel to flow to the pilot-burner I8 and also in the main fuel pipe i2 as far as the electromagnetic valve i6 which is normally closed. As the main switch is also operated to closed position as described when valve lil is opened, an electrical circuit is established which may be traced as follows: From the secondary of the transformer 28 to wire 90, main switch of valve I 4, wire 92, coil 34 of the relay 38, wire 94, cut-out 14, wire 96, electromagnetic valve I6, wire 96, heater coil im) of purge bimetal switch Bil, wire m2', wire lud, ballast resistor 56 and wire it back to the secondary of the transformer 28. All of the foregoing elements are in series circuit. A second series circuit is established at the same time by way of wire Hi8 which is connected to wire 92 at point designated "B," armature 3c, contacts i0 and #32, wire lili, signal lamp l2, and wire M2 connected to wire it. arrangements are modified immediately by the. instantaneous pick-up of the relay il@ so that thereis insuicient time for the signal lamp l2 to light or the electromagnetic valve it to be actuated to open position.

Energization of the coil 3ft of the control relay 30 in the circuit described will attract the armatures 36 and 38 and cause engagement of contacts iS-52 and 5-5, respectively. In this contact position, which may be termed the pickup position, the signal lamp circuit is open and the ignition coil circuit is closed. Moreover, by

vclosing of contacts S--d the cut-Out ld, electroin the unheated condition of the bimetal arm t2 of the purge bimetal switch t@ the contacts @li-6b are closed. Thus, two circuits are established in the pick-up position of the control relail as follows: One circuit may be traced from point designated B to the relay coil 3S by wire 92, from the relay coil 3d by wire tl, wire lili, contacts iid-5d, armature 3B, wire M32, wire Hifi, ballast resistor 56 and wire tilt back to point A." The other circuit from point B comprises wire Mld, armature 36, contacts i352, heater coil it@ of shunting bimetal switch t2, wire liti, contacts tft-t6 of purge bimetal switch tt, wire H20, adjusting resistor mvv/ire l22, wire i265, ignition coil Z2, wire 26, and wire 92d to wire Mit back to the point A. -As in the previous position of the control relay f3@ all of the elements in each of the two circuits are in series circuit.

The ignition means 22 ignites the fuel flowing from the pilot burner i8 causing the ballast resistor 56 to become heated in response to the flame thereof. Meanwhile, the heater coil i l 6 of bimetal switch 82 has caused warping of this These circuit 4 of contacts 88-,88 the armatures 88 and I8 of the relay resume their normal positions. Hence, the circuit arrangements first described are resumed and the electromagnetic valve I8 is actuated to open position to permit flow of fuel to the main burner I Il where it is ignited bythe pilot flame.

, The arrangement thus accomplishes'two pur-` poses. In the first place, the full sensitivity of the relay is used for pick-up of the armatures 88 and Il as ballast resistor 88 is unheated and the shunting resistor 88 is not at such time closed in the circuit including coil 84 by virtue of the open contacts 88-88. In the second place, the bimetal switch 82 introduces the shunting resistor 80' after thel ballast resistor 88 has had time to become heated by the pilot flame so that the relay current is changed from a value above "drop-ofi to a value below drop-off at an accelerated Vrate by the joint action of these elements. The arrangement described avoids the necessity of relying upon variation in the current to the relay caused solely by heating of the ballast resistor 88, as this cannot be made sufncient for quick response due to the necessary balancing of current values in the low voltage, low resistance circuit which is used to economize on power consumption. Ihe avoidance of a slow decrease in relay current through release value eliminates objectionable noise in operation.

If the ballast resistor is not heated by a flame the shunting eect due to closing of the contacts 88 and 88 is not sufficient to cause dropping of the relay armatures. The valve I8 therefore remains closed and flow of fuel vto main burner Ill is prevented. Should the main and pilot burners become extinguished during normal running condition, a recycling operation will occur due to cooling of the ballast resistor 58. As the resistance of the ballast resistor decreases upon cooling thereof, the current through the operating coil 34 of the control relay 80 becomes large enough to attract the armatures 88 and 88 causing the elecromagnetic valve I8, cut-out 14 and heater coil I00 of bimetal switch 80 to be shortcircuited by the circuit established by the contact engagement previously described. In the period between extinguishment of the burner flames and the picking up of the relay, the iio'w of fuel tothe main burner continues. However, when the relay picksup causing the electromagnetic valve to be short-circuited the fuel flow to the main burner is thereupon cut-off.

It will be apparent that the purge bimetal switch 80 has its contacts 8| and 88 open at the time that the control relay picks up. There is thus a period between the time of pick-up and the closing of these contacts in which no fuel may flow to the main burner and the ignition means 22 is deenergized. It is apparent that the bimetal switch 80 is so designed that-its cooling period is longer than that of the ballast resistor 58 so as to allow a suitable period between the time of closing of the electromagnetic valve I8 and energizing of the ignition means 22 by operation of the bimetal switch 80 to permit any unburned fuel from the main burner I0 to flow away. When the bimetal purge switch contacts close, the ignition means 22 is energized, the fuel flowing from the pilot burner I8 is ignited and the foregoing sequency of operation proceeds.

By placing the contacts 84 and 88 of the purge bimetal switch in series circuit with the ignition means 22, a more eiiicient use can be made of the ballast resistor 88 and less power consumed in opannui erating the system than in other possible' ax'- rangements. It is apparent that as in a recycling operation the purge switch contacts are open and the ballast resistor 88 must be cooled to effect pick-up of the armatures, then the circuit of the ignition means causes no drop in secondary voltage. In the case of a cold start the purge switch contacts are closed, but vas the other circuit elements are also cold, there is suiiicient current available for immediate pick-up. It is, of course, desirable to have the maximum power available in the relay circuit at the time of pickup. However, when the bimetal 82 of this switch cools so as to close the contacts and so connect the ignition means, then some transformer voltage drop mayadvantageously be used to reduce the release time of the control relay I8. By using a relatively small capacity transformei` 28 to take advantage of this reduction in release time, it becomes necessary to introduce an additional switch in the system, to be operated manually in case the ignition means burns out. Thus, the switch 18 is used to introduce additional resistance 18 equivalent to that of the ignition means 22 in case of failure of the ignition means and the pilot burner can then be ignited -by a match, although the system would not then recycle.

The cut-out Il is connected in the circuitso that it is short-circuited by the relay contacts which short-circuit the electromagnetic valve I8. Thus. during the starting period when all the circuit elements are cold and the relay circuit current is relatively largel the fuse is short-circuited. Protection against escape of unburned fuel from the main burner is unnecessary as long as the electromagnetic valve is also short-circuited. -This location of the cut-out is therefore satisfactory as it is operable at all times except when the electromagnetic valve is short-circuited.

While a preferred embodiment of the invention has been shown and described, it is apparent that many modifications will occur to those skilled in the art. Hence, the invention is not to be deemed limited to the form shown and described or otherwise than as included in the scope of the claims appended hereto.

I claim: y l

1. A safety control forfuel burners having main and pilot burners, comprising electrically operable means movable between positions for controlling the supply of fuel to the main burner, an energizing circuit for said movable means, electrically operable switching means in said circuit responsive to variations in the current value supplied thereto for causing movement of said movable means between said positions, a thermal resistance element in said circuit adapted to vary inresistance value to vary the current value supplied to said switching means in response to the presence or absence of a ilame at the pilot burner,

means electrically connected to said switching means and cooperable with said element for causing variations in the current value supplied to said switching means suiilcient to change the position of said movable means when said element is heated by the pilot burner name, and means controlled by said switching means for rendering the lastsaid means effective after said resistance element has had time to become heated and` thereby changing the position of said movable means.

2. A safety control for fuel burners having main andpilot burners, comprising electrically' operable means movable between open and closed 1 positions for controlling the supply oi i'uel to the main burner,l an energizing circuit for said controlling means, a control relay in said circuit responsive to variations in the current value supplied thereto and having both normally open and normally closed contacts, said controlling means being actuated to open position in said normal contact position and being movable to closed position upon operation of said relay to reverse said normal contact position, a main switch lor closing the circuit of said controlling means andcausing said relay operation to said reversed contact position. a thermal resistance element in said circuit having a preselected temperature coei'iicient of resistance and adapted to reduce the current supply to said relay upon an increase in resistance of said element in response to heating thereof by a llame at the pilot burner, means electrically connected to. said relay and cooperable with said heated element for reducing the current value to said relay below that required to maintain reversed contact position, and means operable in said reversed contact position for rendering the last said means effective after said resistance element has had time to become heated, whereby said normal contact position is restored and said controlling means actuated to open position.

3. A safety control for fuel burners having main and pilot burners, comprising electrically operable means movable between positions for controlling the supply of fuel to the main burner, electrically operable switching means controlling a circuitfor said movable means and responsive to variations in the current value supplied to said switching means for. causing movement of said'movable means between said positions, a thermal resistance element responsive to a llame f at said pilot burner and connected in said cir' cuit for varying the current value supplied to said switching means upon variations inthe resistance of said element due to the presence or absence of said llame, and means establishing a shunt around said switching means which is ef- 4. A safety,A control for fuel burners havingmain and pilot burners, comprising electrically operable means movable 'between positions for controlling the supply of fuel to the main-burner, relay contacts having a closed position for establishing a shunt around said movable means and.- being biased to open position, loperating means for said relay contacts in series circuit with said movable means and adapted to close said contacts when current of suiilcient value is sup- .plied to y said opearting means, said movable means being thereby maintained in one position, means responsive to a llame at the P11012 burner and connected in said series circuit for varying the current value supplied to said operating means but insuiilciently to cause return of said contacts to biased position upon a variation in the resistance of said llame responsive means when heated by said'iiame, and means establishing a shunt around said operating means which is effective when said llame responsive means is heated by said flame and cooperating therewith to vary the value of the current supply to said operating means sufficiently to release said contacts to biased position and thereby cause movement of said movable means to another position.

5. A safety control for fuel burners having y 8 t main and pilot burners. comprising electrically operable means movable between positions for controlling the supply oi' fuel to the main burner.

ilrst and second relay contacts, said flrstrelay contacts having a closed position for establishing a shunt around said movable means and being biased with said second relay contacts to open position, operating means for said relay contacts in series circuit with said movable means and adapted to close said contacts when current of suiiicient value `is supplied to1 said operating means, said movable means being thereby maintained in onel position, a thermal resistance element having a preselected temperature coeiilcient oi' resistance connected in series circuit with said movable means and located' in proximity of the pilot burner llame for varying in resistance when l i sition, a thermally operatedswitch for closing said parallel circuit, and a'heater responsive to closure of said second relay contacts for causing said switch operation and thereby introducing said resistor after said thermal resistance element has had time to become heated.

6. An electromagnetic switching device for fuel burners comprising a pilot burner, a magnet coll energized from a source of current supply, an

amature movable into attracted relation with said coil upon current of sufilcient value being supplied thereto, said armature being biased to unattracted relation but being maintsinsble'in said attracted relation upon current of a lesser "value being supplied to said coil, relay contacts associated with said armature and being closed when said armature is in attracted position, means introduced in the energizing circuit of said coil -by closing of said contacts and responsive .to a llame at said burner for reducing the current supply to said coil to said lesser value and means cooperable with said rllame responsive means for reducing the current supply to said coil below said lesser value, said last means establishing a shunt around said magnet coil and thereby causing immediate movement of said armature to' unattracted position if said flame responsive means is responding to the name.

7. An electromagnetic switching device for fuel burners comprising a pilot burner, a magnet coil energized from a source of current supply, an armature movable into attracted relation with said coil upon current of suillcient value beinlz'v supplied thereto, said amature bein-g biased to unattracted relation but being maintainable in said attracted relation upon current of a lesser value being supplied to said coil, a plurality of relay contact pairs associated with said armature and being closed when said armature is in attracted position, means introduced in the energizing circuit of said coil by closing of a pair of said contacts and responsive to a llame at said coil below said lesser value and thereby causing immediate movement of said amature to unattracted position if s'aid flame responsive means is responding to the flame.

8. A fuel burner control system comprising a burner, a thermal resistor responsive to the presence of a flame at the burner, a relay, a plurality of pairs of contacts associated with said relay, a source of current supply, a main switch operable for connecting said relay to said sourceto cause operation of said relay and complete two parallel circuits through different pairs of said relay ccntacts, one said circuit including said thermal resistor,.the other said circuit including means for closing one of said pairs of contacts, and means for establishing a shunt around said relay by closure of said one of said pairs of contacts, said shunt cooperating with said thermal resistor when said resistor is being heated by said flame for reducing the current value to said relay and causing another operation thereof to open said circuits and render said closure means inoperative.

9. A fuel burner control system comprising a main burner, a pilot burner, electrically operable means controlling the flow of fuel to the main burner, a relay havin-g a coil in series .circuit with said controlling means, first relay contacts for establishing a shunt around said controlling means when said coil is initially energized in relay pick-up position, a thermal resistor in series circuit with said controlling means, said resistor having a positive temperature coelc'ient of resistance and being responsive to the flame of the pilot burner for increasing in resistance value and reducing the current value to said relay coil, an electric igniter in parallel circuit with said controlling means and relay coil, second relay contacts controlling said parallel circuit and operable to close said parallel circuit and cause energization of said igniter in said relay pick-up position, a first thermal switch in-series circuit with said igniter and being closed in said relay pick-up position, means in series circuit with said controlling means and likewise shunted by said first relay contacts, said last means being adapted upon removal of said shunt therefor for operating said switch to open position and maintaining it open for a predetermined period following reestablishment of said shunt, a second thermal switch for shunting said relay coil and being open in said relay pick-up position, and means in series circuitwith said igniter and controlled by said second relay contacts for operating said second switch to closed position and thereby further reducing the current value to said relay coil to cause operation of said first and second relay contacts from said pick-up position if said thermal resistor is heated, said last operation removing the shuntfrom said controlling means to cause operation of the same'to permit fuel llow to the main burner and simultaneously deenergizing said isn'iter, said first thermal switch remaining open for said predetermined period and establishing a purge period for the main burner upon a recycling operation causing said reestablishment oi' said shunt.

10. A control system for an electrical circuit comprising electrically operable means for controlling an operation, a relay having a coll and a switch operable thereby for controlling said means upon a sufficient variation in .the energy value supplied to said coil, said switch being inif l0 being short-circuitedby said switch when said circuit is closed, said switch being subsequently operable for closing a second circuit including said coil and said means when said energy is reduced to a value insufilcient to maintain said rst circuit closed, and resistance means operatively associated with said switch for shunting -said coil when said first circuit is closed and reducing said energy value below said sufficient value .but above that at which said second circuit is closed, said resistance means being electrically disconnected by said subsequent operation of said switch.

11.111 a control system having a source of electrical energy, an electromagnetic relay connected to the source and having a coll and a plurality of normally open contacts, said contacts being operable to closed position upon energy of suiiicient value being supplied to said coil, electrically energizable means connected to the source and said relay for eiective deenergization in said closed position of certain of said contacts and for energization in Isaid open contact position, a timing switch having operating means therefor adapted to cause closure ofsaid switch in said closed position of other of-said contacts, and a'shunt for said coil comprising resistance means connected in parallel circuit with said coil and in yseries circuit with said timing switch Afor energization in said closed posit/ion of said other contacts, said resistance means being adapted for reducing the energy value supplied to said coil below that which is supplied thereto in said open contact .position but above that Awhich would cause operation of said cont-acts to said open position.

12. In a control system having a source of electrical energy, an' electromagnetic relay connected to the source and having at least -two pairs of normally open contacts, said contacts being jointly operable ,to closed .position upon energy of sulcient value being supplied to said coil, electrically energizable means connected to the source in series circuit with said .coil and in parallel circuit with one of said pairs of contacts, said means being shunted by said one pair of contacts in said closed position thereof and thereby effectively deenergized, a timing switch having operating means therefor connected to the source in parallel circuit with said coil and electrically energizable means adapted -to cause closure of said switch in said closed position of lthe other pair of said contacts, and a shunt for said coil comprising resistance means connected in parallel circuit with said coil and in series with said timing switch for energization in said closed position of said other contact pair, said resistance means being adapted for reducing the energy value supplied to said coil below that which is supplied thereto in said open contact Position but above that which would cause operation ofsaid contacts to said open position.

CHARLES K. STROBEL.

REFERENCES CITED The following references are of record in the i'lle of this patent:

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